mk dùng p2 tách hạng tử ko bt đúng ko nha
A = x^2 - 4x -5
A = x^2 - 4x - x -4
A = x ( x - 1 ) - 4( x - 1)
A = ( x -1 ) . (x - 4)
câu b chờ mk suy nghĩ
\(A=x^2-4x-5=x^2-4x+4-9=\left(x-2\right)^2-3^2\)
\(=\left(x-2-3\right)\left(x-2+3\right)=\left(x-5\right)\left(x+1\right)\)
\(B=4x^2-4x-15=4x^2-4x+1-16=\left(2x-1\right)^2-4^2\)
\(=\left(2x-1-4\right)\left(2x-1+4\right)=\left(2x-5\right)\left(2x+3\right)\)
Cách 2:
\(A=x^2-4x-5=x^2-5x+x-5=x\left(x-5\right)+\left(x-5\right)\)
\(=\left(x-5\right)\left(x+1\right)\)
\(B=4x^2-4x-15=4x^2-10x+6x-15=2x\left(2x-5\right)+3\left(2x-5\right)\)
\(=\left(2x+3\right)\left(2x-5\right)\)
